1. Field of the Invention
The present invention relates to a method for operating a spark ignition, direct injection gasoline engine to control the formation of deposits on the fuel injectors by combustion in said engine of a fuel characterized as a gasoline of particular composition.
2. Description of the Related Art
Gasoline direct injection (GDI) engine technology has been investigated for about 80 years, but injector coking is still a major concern. Because gasoline direct injection engines have a fuel economy benefit of 15-30% and result in the production of lower levels of greenhouse gas CO2 emissions and exhibit a power improvement of 5-15% per unit volume of engine displacement, they have continued to be investigated and developed despite the technical challenges of fuel management control, engine deposits, exhaust emissions control and injector fouling. An especially attractive feature of gasoline direct injection engines is the reduction in the octane requirement of the engine. Because of in-cylinder fuel evaporation and resulting charge cooling effect, up to a six number lower octane requirement can be exhibited by a GDI. However, as previously stated, and despite the advantages demonstrated by GDI engines, early GDI engines such as the Texaco TCP of 1951 and the Ford PROCOS of 1968 suffered from severe deposit problems which contributed to the demise of those programs.
Gasoline direct injector engines, however, have continued to be developed in Japan and Europe. Mitsubishi, Toyota, Nissan, Honda, Mazda, Renault and VW have all indicated a commitment to pursuing GDI engine technology and commercializing vehicles powered by GDI engines.
However, injector fouling will continue to be an area of concern for manufacture and vehicle owner.